Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable medical device system.
As shown in FIG. 1, a SCS system typically includes an Implantable Pulse Generator (IPG) 10, which includes a biocompatible device case 12 formed of a conductive material such as titanium for example. The case 12 typically holds the circuitry and battery 14 necessary for the IPG to function. The IPG 10 is coupled to distal electrodes 16 designed to contact a patient's tissue. The distal electrodes 16 are coupled to the IPG 10 via one or more electrode leads (two such leads 18 and 20 are shown), such that the electrodes 16 form an electrode array 22. The electrodes 16 are carried on a flexible body 24, which also houses the individual signal wires 26 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 18, labeled E1-E8, and eight electrodes on lead 20, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 18, 20 contain proximal electrode contacts 29, which couple to the IPG 10 using lead connectors 28 fixed in a non-conductive header material 30 such as an epoxy.
As shown in the cross-sections of FIGS. 2A and 2B, an IPG 10 typically includes an electronic substrate assembly including a printed circuit board (PCB) 32, along with various electronic components 34 mounted to the PCB. A telemetry coil 36 is used to transmit/receive data to/from an external controller (not shown). In these examples, the telemetry coil 36 is within the case 12, as disclosed in U.S. Pat. No. 8,577,474, although it can also be placed in the header 30 in other examples.
IPGs can differ in the type of battery 14 employed. FIG. 2A shows an IPG 10a that contains a rechargeable secondary battery 14a. To facilitate recharging of battery 14a, the IPG 10a contains an additional charging coil 38. As shown in FIG. 3, charging coil 38 allows an external charger 50 to provide power 90 to recharge the battery 14a when necessary. As one skilled in the art will understand, such means of charging battery 14a using an external charger 50 occurs transcutaneously via magnetic induction: the external charger 50 is turned on, and an AC current is generated in coil 52 in the external charger. This produces an AC magnetic field 90, which induces an AC current in charging coil 38 in the IPG 10a. This current is rectified to a DC level in the IPG 10a, and used to recharge the battery 14a. Rechargeable batteries 14a can be formed using different chemistries, but lithium ion polymer batteries are popular for use in implantable medical devices, and produce voltages of about 4.2 Volts.
FIG. 2B, by contrast, shows an IPG 10b that contains a non-rechargeable primary battery 14b, i.e., one in which the electrochemical reaction is not reversible by passing a charging current therethrough. Because battery 14b is not rechargeable, there is no need for a charging coil (compare 38 in FIG. 2A) in IPG 10b. However, primary batteries use up the materials in one or both of their electrodes, and thus have a limited life span. Once the battery 14b is exhausted, it will be necessary to explant IPG 10b from the patient, so that the battery 14b can be replaced and the IPG 10b re-implanted, or so that a new IPG 10b with a fresh battery 14a can be implanted. Primary batteries 14b can be formed using different chemistries, but Lithium CFx batteries, or Lithium/CFx-SVO (Silver Vanadium Oxide) hybrid batteries are popular for use in implantable medical devices, and produce voltages of 1.2-3.2 Volts.
It is easy to assume that a patient should always be provided an implant with a rechargeable battery to permit charging when needed without the need of explantation, but there are also good reasons to prefer an implant with a non-rechargeable primary battery. Primary batteries are typically cheaper than rechargeable batteries, and may not suffer from reliability concerns inherent with rechargeable batteries. Moreover, use of a primary battery in an implant saves costs in other ways: the implant need not contain the overhead of a charging coil (38, FIG. 2A), and an external charger 50 (FIG. 3) can be entirely dispensed with. Moreover, the patient is convenienced by having an implant with a primary battery, as she will not have to concern herself with charging it. The case of a primary-battery implant may also be smaller than a rechargeable-battery implant, which would also convenience the patent.
As the inventors recognize, a clinician currently has little guidance to know in advance whether a given patient would most likely benefit from having an implant with a rechargeable battery 14a, or from having an implant with a primary battery 14b. This disclosure provides solutions.